The present invention relates to an aqueous coating composition providing improved adhesion to friable surfaces such as chalky weathered paint surfaces and masonry surfaces and to a method for producing a coating on a friable surface.
Coatings are frequently desirably applied to surfaces which are both porous and weak, i.e., subject to attrition on abrasion such as, for example, chalky surfaces of coatings which have weathered to an extent that poorly consolidated pigment forms a surface layer on the coating and masonry surfaces, weathered or not, which have a poorly consolidated surface. A substrate to which a coating is applied may have an entirely friable surface or only portions of the surface may be friable. Such substrates present a problem to the applicator in that, without being bound by this mechanism, the aqueous coating composition may not penetrate the weak boundary layer of the friable surface or friable surface areas sufficiently to provide a dry coating with the requisite degree of adhesion to the substrate below the weak surface.
U.S. application Ser. No. 4,771,100 discloses the use of ethoxylated fatty amines in the preparation of single stage latexes containing about 0.1 to 10 weight percent of copolymerized carboxylic acid monomer which have particle sizes between 889 and 1091 Angstroms for use as coatings. No use of these single stage latexes, in combination with ethoxylated fatty amines, to improve adhesion to friable surfaces was disclosed.
U.S. application Ser. No. 5,035,944 discloses a method for treating surfaces, including those of wood, plastic, and cementitious substrates to provide coatings having superior appearance with respect to gloss and hardness. The substrates were treated with aqueous coating compositions including particles of polymer of size 20 to 70 nanometers, having at least two mutually incompatible copolymers in separate phases. The outer portion of the particle was predominately a phase containing a copolymer having a Tg significantly lower than that of copolymer making up the predominate phase of the inner portion (core) of the particle. Preferably, the outer phase copolymer had a low Tg of less than 35xc2x0 C., while the inner (core) phase copolymer had a high Tg of at least 45xc2x0 C. The copolymer of the outer phase had a weight average molecular weight (Mw) of 50,000 to 10,000,000, while the copolymer of the inner (core) phase of the particle had an Mw of 1,000,000 to 10,000,000. The disclosed particles achieve improved hardness while maintaining good film forming performance by surrounding an inner (core) phase polymer that is hard (i.e., having Tg well above room temperature, and molecular weight of at least 1,000,000) under ambient conditions with an outer phase polymer that is soft and flowable (i.e., having Tg near or below room temperature, and Mw as low as 50,000). No use of these multi-stage latexes to improve adhesion to friable surfaces was disclosed.
We have now prepared aqueous coating compositions including, dispersed therein, a plurality of polymeric particles having an average particle size of less than 120 nanometers, each polymeric particle including at least one polymer A and at least one polymer B. Polymer A contains, as polymerized units, substantial amounts of acid functional monomers, water soluble monomers, or both. The total amount of acid functional monomers, or water soluble monomers, or both, contained, as polymerized units, in Polymer B is less that the total amount contained in Polymer A. We have, surprisingly, found that these compositions exhibit improved adhesion to chalky weathered surfaces when compared with aqueous coating compositions in which the polymeric particles have been prepared in a single polymerization stage. We have also discovered that the presence of nonionic surfactants further improves the adhesion to chalky weathered surfaces observed for aqueous coating compositions containing the plurality of polymeric particles, each of which includes at least one polymer A and at least on polymer B.
Used herein, these terms, enclosed in quotation marks, are defined as follows:
xe2x80x9cfriable surfacexe2x80x9d refers to porous, weak surfaces subject to attrition on abrasion and includes: chalky surfaces of coatings which have weathered to an extent that poorly consolidated pigment forms a surface layer on the coating; masonry surfaces, weathered or fresh, which have a poorly consolidated surface; wall board; weathered uncoated wood; and gypsum.
xe2x80x9cpolymerization stagexe2x80x9d refers to the time interval during which a monomer or a mixture of monomers is polymerized to form polymer;
the xe2x80x9cpolymeric particlesxe2x80x9d have an average particle size of less than 120 nanometers, exist in large numbers (i.e., as a xe2x80x9cplurality of polymeric particlesxe2x80x9d) and are prepared by emulsion polymerization accomplished in two or more polymerization stages, at least one polymerization stage of which produces xe2x80x9cpolymer Axe2x80x9d, and at least one polymerization stage of which produces xe2x80x9cpolymer Bxe2x80x9d;
xe2x80x9cPolymer Axe2x80x9d is characterized in that it has either a higher acid number compared to xe2x80x9cpolymer Bxe2x80x9d, or that it is prepared from a monomer mixture containing 5-99.5% of at least one water soluble monomer, or both; and
xe2x80x9cwater solublexe2x80x9d means that the monomer has a water solubility of 8% or more by weight, based on the weight of water, as calculated by the QSAR Method (see Table A below).
xe2x80x9cAcid numberxe2x80x9d is a convenient indicator of the amount of acid functionality contained in a polymer. xe2x80x9cAcid numberxe2x80x9d is defined as the number of milligrams of potassium hydroxide required to neutralize the free acid in one gram of polymer solids.       Acid    ⁢          xe2x80x83        ⁢    Number    =            (              mg        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        KOH            )              (              g        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        polymer        ⁢                  xe2x80x83                ⁢        sample            )      
The present invention relates to an aqueous coating composition having improved adhesion to friable surfaces including a plurality of polymeric particles, each of said particles including:
(a) at least one polymer A having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer A is an emulsion polymer consisting essentially of:
(i) at least one copolymerized ethylenically unsaturated nonionic monomer having a water solubility less than 8% by weight, based on the weight of water; and
(ii) at least one copolymerized acid monomer, such that the acid number of said polymer A is 13 to 260; and
(b) at least one polymer B having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer B is an emulsion polymer including, as polymerized units, at least one ethylenically unsaturated nonionic monomer,
wherein said particles have an average particle diameter less than 120 nanometers.
A second aspect of the present invention relates to an aqueous coating composition having improved adhesion to friable surfaces including a plurality of polymeric particles, each of said particles including:
(a) at least one polymer A having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer A is an emulsion polymer including:
(i) 5-99.5% by weight, based on said polymer A weight, of at least one copolymerized ethylenically unsaturated first nonionic monomer having a water solubility of 8% or more by weight, based on the weight of water;
(ii) 0-94.5% by weight, based on said polymer A weight, of at least one copolymerized ethylenically unsaturated second nonionic monomer having a water solubility of less than 8% by weight, based on the weight of water; and
(iii) at least one copolymerized acid monomer, such that the acid number of said polymer A is 3 to 100; and
(b) at least one polymer B having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer B is an emulsion polymer including, as polymerized units, at least one ethylenically unsaturated nonionic monomer,
wherein said particles have an average particle diameter less than 120 nanometers.
A third aspect of the present invention relates to a method for producing a coating on a friable surface including:
(1) applying to said friable surface a layer of an aqueous coating composition including a plurality of polymeric particles, each of said particles including:
(a) at least one polymer A having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer A is an emulsion polymer consisting essentially of:
(i) at least one copolymerized ethylenically unsaturated nonionic monomer having a water solubility less than 8% by weight, based on the weight of water; and
(ii) at least one copolymerized acid monomer, such that the acid number of said polymer A is 13 to 260; and
(b) at least one polymer B having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer B is an emulsion polymer including, as polymerized units, at least one ethylenically unsaturated nonionic monomer,
wherein said particles have an average particle diameter less than 120 nanometers; and
(2) drying said coating composition.
A fourth aspect of the present invention relates to a method for producing a coating on a friable surface including:
(1) applying to said friable surface a layer of the aqueous coating composition including a plurality of polymeric particles, each of said particles including:
(a) at least one polymer A having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer A is an emulsion polymer including:
(i) 5-99.5% by weight, based on said polymer A weight, of at least one copolymerized ethylenically unsaturated first nonionic monomer having a water solubility of 8% or more by weight, based on the weight of water;
(ii) 0-94.5% by weight, based on said polymer A weight, of at least one copolymerized ethylenically unsaturated second nonionic monomer having a water solubility of less than 8% by weight, based on the weight of water; and
(iii) at least one copolymerized acid monomer, such that the acid number of said polymer A is 3 to 100; and
(b) at least one polymer B having a glass transition temperature of xe2x88x9220xc2x0 C. to 100xc2x0 C.,
wherein said polymer B is an emulsion polymer including, as polymerized units, at least one ethylenically unsaturated nonionic monomer,
wherein said particles have an average particle diameter less than 120 nanometers; and
(2) drying said coating composition.
In any of the aforementioned aspects of the present invention, the aqueous coating composition may further include at least one nonionic surfactant in the amount 0.25 to 10 weight percent, based on the total dry weight of the polymeric particles.
The aqueous coating composition of the present invention includes a plurality of polymeric particles. Each polymeric particle includes a polymer A and a polymer B. Polymer A and polymer B are formed in separate emulsion polymerization stages. There may be more than one polymer A and more than one polymer B. In fact, polymer formed in a separate stage and dissimilar from polymer A or polymer B (e.g., one having a Tg above 100xc2x0 C.) may also be present in the particles. Polymer A may be prepared in a polymerization stage either before or after the polymerization stage in which polymer B is prepared. Where there is more than one polymer B, polymer A, or more than one of each, the polymerization stages in which they are formed may be carried out in any order. The glass transition temperatures of both polymer A and polymer B are xe2x88x9220xc2x0 C. to 100xc2x0 C. Although it is not a requirement of the present invention, it is preferred, and will usually be the case, that polymer A and polymer B are mutually incompatible. When this incompatibility exists, the polymeric particles may be present in the following morphological configurations, for example, core/shell, core/shell particles with shell phases incompletely encapsulating the core, core/shell particles with a multiplicity of cores, interpenetrating network particles, and the like. In all of these cases, the majority of the surface area of the particle will be occupied by at least one outer phase and the interior of the particle will be occupied by at least one inner phase. The mutual incompatibility of the two polymer compositions may be determined in various ways known in the art. The use of scanning electron microscopy using staining techniques to emphasize the difference between the appearance of the phases, for example, is such a technique.
Particle sizes herein are those determined using a Brookhaven Model BI-90 particle sizer manufactured by Brookhaven Instruments Corporation, Holtsville N.Y. Reported as xe2x80x9ceffective diameterxe2x80x9d.
Glass transition temperature, Tgs, used herein are those calculated by using the Fox equation (T. G. Fox, Bull. Am. Physics Soc., Volume 1, Issue No. 3, page 123(1956)), that is, for calculating the Tg of a copolymer of monomers M1 and M2,
1/Tg(calc.)=w(M1)/Tg(M1)+w(M2)/Tg(M2) 
,wherein
Tg(calc.) is the glass transition temperature calculated for the copolymer
w(M1) is the weight fraction of monomer M1 in the copolymer
w(M2) is the weight fraction of monomer M2 in the copolymer
Tg(M1) is the glass transition temperature of the homopolymer of M1
Tg(M2) is the glass transition temperature of the homopolymer of M2, all temperatures being in xc2x0 K.
The glass transition temperatures of homopolymers may be found, for example, in xe2x80x9cPolymer Handbookxe2x80x9d, edited by J. Brandrup and E. H. Immergut, Interscience Publishers.
Aqueous emulsion polymerization is the preferred method of preparing the polymeric particles because it can produce the desired particle size of less than 120 nanometers. However, any polymerization method that would allow preparation of an aqueous dispersion of polymeric particles having the desired size and each containing both polymer A and polymer B, produced in separate polymerization stages, would be acceptable. Polymeric particles prepared by emulsion polymerization are usually stabilized by adding anionic, nonionic, cationic, or amphoteric surfactants, or by the incorporation of anionic or cationic moieties into the backbone of the polymer itself during synthesis. The emulsion polymerization can be carried out by a number processes such as those described in Blackley, D. C. Emulsion Polymerisation; Applied Science Publishers: London, 1975; Odian, G. Principles of Polymerization; John Wiley and Sons: New York, 1991; Emulsion Polymerization of Acrylic Monomers; Rohm and Haas, 1967.
Aside from the specific compositional requirements for polymer A, to be described later, the following description of compositions and methods of preparation for an emulsion polymer are common to both polymer A and polymer B. The monomers from which these emulsion polymers are formed are ethylenically-unsaturated. When they polymerize in the presence of free radical initiators, these ethylenically-unsaturated monomers form addition polymers. The aqueous emulsion polymer may be prepared by conventional techniques known to those of ordinary skill in the art. The polymer may contain, as polymerized units, ethylenically unsaturated monomers. Examples of these ethylenically unsaturated monomers include: C1-C22 linear or branched chain alkyl (meth)acrylates, bornyl (meth)acrylate, isobornyl (meth)acrylate, and the like; hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; (meth)acrylamide or substituted (meth)acrylamides; styrene or substituted styrenes; butadiene; vinyl acetate or other vinyl ester; N-butylaminoethyl (meth)acrylate, N,N-di(methyl)aminoethyl (meth)acrylate; monomers containing xcex1,xcex2-unsaturated carbonyl functional groups such as fumarate, maleate, cinnamate and crotonate; (meth)acrylonitrile; and acetoacetoxyethyl (meth)acrylate. Used herein, the word fragment xe2x80x9c(meth)acrylxe2x80x9d refers to both xe2x80x9cmethacrylxe2x80x9d and xe2x80x9cacrylxe2x80x9d. For example, (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and methyl (meth)acrylate refers to both methyl methacrylate and methyl acrylate.
Acid-functional monomers may also be present in the aqueous emulsion polymer as polymerized units. Acid-functional monomers useful in the present invention include, for example, (meth)acrylic acid, itaconic acid, crotonic acid, phosphoethyl (meth)acrylate, sulfoethyl (meth)acrylate, 2-acrylamido-2-methyl-1-propanesulfonic acid, fumaric acid, maleic anhydride, monomethyl maleate, and maleic acid.
Optionally, a low level of a multi-ethylenically unsaturated monomer may be incorporated into the polymer to provide crosslinking. The level of multi-ethylenically unsaturated monomer may be 0-5% by weight, based on the weight of the dry emulsion polymer. The upper limit is typically determined by the point at which film formation becomes impaired. Useful multi-ethylenically unsaturated monomers include, for example, allyl (meth)acrylate, diallyl phthalate, 1,4-butylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,1,1-trimethylolpropane tri(meth)acrylate.
Conventional surfactants may be used to stabilize the emulsion polymerization systems before, during, and after polymerization of monomers. These conventional surfactants will usually be present at levels of 0.1 percent to 6 percent by weight based on the weight of total monomer. At least one anionic, nonionic, or amphoteric surfactant may be used, or mixtures thereof. Examples of anionic emulsifiers include sodium lauryl sulfate, sodium dodecyl benzene sulfonate, dioctylsulfosuccinate, sodium polyoxyethylene lauryl ether sulfate, and sodium salt of tert-octylphenoxyethoxypoly(39)ethoxyethyl sulfate. Examples of nonionic surfactants include glycerol aliphatic esters, oleic acid monoglyceride, polyoxyethylene aliphatic esters, polyoxyethylene glycol monostearate, polyoxyethylene cetyl ether, polyoxyethylene glycol monolaurate, polyoxyethylene glycol monooleate, polyoxyethylene glycol stearate, polyoxyethylene higher alcohol ethers, polyoxyethylene lauryl ether, polyoxyethylene nonylphenol ether, polyoxyethylene octylphenol ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylenesorbitan aliphatic esters, polyoxyethylenesorbitan monolaurate, polyoxyethylenesorbitan monooleate, polyoxyethylenesorbitan monopalmitate, polyoxyethylenesorbitan monostearate, polyoxyethylenesorbitan trioleate, polyoxyethylenesorbitan tristearate, polyoxyethylenesorbitol tetraoleate, stearic acid monoglyceride, tert-octylphenoxyethylpoly(39)ethoxyethanol, and nonylphenoxyethylpoly(40)ethoxyethanol.
Amphoteric surfactants may also be utilized solely, or in combination with anionic surfactants, nonionic surfactants, or mixtures thereof, to stabilize particles of the polymer during and after aqueous emulsion polymerization, or other dispersion polymerizations. For the purpose of stabilizing particles of polymer in aqueous systems, amphoteric surfactants may be used at levels of 0.1 percent to 6 percent by weight based on the weight of total monomer. Useful classes of amphoteric surfactant include aminocarboxylic acids, amphoteric imidazoline derivatives, betaines, and macromolecular amphoteric surfactants. Amphoteric surfactants from any of these classes may be further substituted with fluorocarbon substituents, siloxane substituents, or combinations thereof. Useful amphoteric surfactants can be found in Amphoteric Surfactants, ed. B. R. Bluestein and C. L. Hilton, Surfactant Series Vol. 12 Marcel Dekker N.Y., N.Y.(1982).
Alternatively, all, or a portion, of the surfactant activity may be provided by initiator fragments, such as those of persulfates, when the fragments become incorporated into the polymer chain.
Incorporating monomers bearing ionic groups into the polymer chain is yet another alternative method of stabilizing the emulsion polymer system. Those monomers bearing ionic groups include the acid-functional monomers described hereinabove.
Initiation of emulsion polymerization may be carried out by the thermal decomposition of free radical precursors, also called initiators herein, which are capable of generating radicals suitable for initiating addition polymerization. Suitable thermal initiators such as, for example, inorganic hydroperoxides, inorganic peroxides, organic hydroperoxides, and organic peroxides, are useful at levels of from 0.05 percent to 5.0 percent by weight, based on the weight of monomers. Free radical initiators known in the art of aqueous emulsion polymerization include water-soluble free radical initiators, such as hydrogen peroxide, tert-butyl peroxide, benzoyl peroxide, t-butyl peroxtoate; alkali metal (sodium, potassium or lithium) or ammonium persulfate; azo initiators such as azobisisobutyronitrile or 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride; or mixtures thereof. Such initiators may also be combined with reducing agents to form a redox system. Useful reducing agents include sulfites such as alkali metal meta bisulfite, or hyposulfite, sodium thiosulfate, or isoascorbic acid, or sodium formaldehyde sulfoxylate. The free radical precursor and reducing agent together, referred to as a redox system herein, may be used at a level of from about 0.01% to 5%, based on the weight of monomers used. Examples of redox systems include: t-butyl hydroperoxide/sodium formaldehyde sulfoxylate/Fe(III); t-butyl hydroperoxide/isoascorbic acid/Fe(III); and ammonium persulfate/sodium bisulfite/sodium hydrosulfite/Fe(III). The polymerization temperature may be 10xc2x0 C. to 110xc2x0 C., depending upon such things as free radical initiator decomposition constant and reaction vessel pressure capabilities.
Frequently, a low level of chain transfer agent such as a mercaptan (for example: n-octyl mercaptan, n-dodecyl mercaptan, butyl or methyl mercaptopropionate, mercaptopropionic acid at 0.05 to 6% by weight based on total weight of monomer) is employed to limit the formation of any significant gel fraction or to control molecular weight.
Polymer A is present in the polymeric particles at preferably 10 to 95 percent, more preferably 30 to 70 percent, and most preferably 40 to 60 percent, by weight, based on the total weight of the polymeric particles, the remainder being substantially polymer B. Therefore, polymer B is present in the polymeric particles at preferably 90 to 5 percent, more preferably 70 to 30 percent, and most preferably 60 to 40 percent, by weight, based on the total weight of the polymeric particles. Polymer A and polymer B are prepared in separate polymerization stages. All of the monomers to be reacted in a given polymerization stage of an aqueous emulsion polymerization (i.e., for either polymer A or polymer B) may be present in the aqueous system at the start of that polymerization stage, or they may be added continuously or intermittently during the course of the polymerization stage. A polymerization stage may alternatively be carried out in such a way that the amounts of monomers, relative to each other, are changed continuously, or continually. The monomers may be added to the aqueous system in neat form, or as a monomer pre-emulsion in which the monomers have been emulsified in water, using surfactants. Free radical initiators may be introduced into the polymerization medium at the start of the polymerization, continuously or intermittently during the polymerization, or some combination thereof. Free radical initiators may further be added at or near the end of the polymerization stage as a chase to cause residual monomers to polymerize.
In the first and third aspects of the invention, the composition of polymer A includes: at least one copolymerized ethylenically unsaturated nonionic monomer having a water solubility less than 8% by weight, based on the weight of water; and at least one copolymerized acid monomer, such that the acid number of polymer A is preferably 13 to 260, more preferably 26 to 195, and most preferably 39 to 130. In the first and third aspects of the invention, the composition of Polymer B must be chosen so that at least 51% of the acid functional monomers contained, as polymerized units, in the polymeric particles reside in polymer A. The acid number of polymer B may be 0 to 65, preferably 0 to 25, more preferably 0 to 15, and most preferably 0 to 7.
In the first and third aspects of the present invention, the composition of polymer B must be chosen so that at least 51% of the acid functionality resides in polymer A.
In the second and fourth aspects of the present invention, the composition of polymer A includes: preferably 5-99.5%, more preferably 8-99.5%, most preferably 20-99.5% by weight, based on polymer A weight, of at least one copolymerized ethylenically unsaturated first nonionic monomer having a water solubility of 8% or more by weight, based on the weight of water; preferably 0-94.5%, more preferably 0-91.5%, and most preferably 0-79.5% by weight, based on polymer A weight, of at least one copolymerized ethylenically unsaturated second nonionic monomer having a water solubility of less than 8% by weight, based on the weight of water; and at least one copolymerized acid monomer, such that the acid number of polymer A is 3 to 100.
In the second and fourth aspects of the present invention, the composition of polymer B must be chosen so that at least 51% of copolymerized ethylenically unsaturated nonionic monomer having a water solubility of 8% or more by weight resides in polymer A.
The water solubility of the nonionic monomers incorporated into the emulsion polymers herein are defined as those determined using the Quantitative Structural Activity Relationship (QSAR) program. The program uses the molecular structure to estimate physical-chemical properties including, molecular weight, vapor pressure, solubility, bioconcentration factor, hydrolysis half-life, Henry""s coefficient, partitioning data, and other parameters (based on Lyman, W., Reehl, W., and Rosenblatt, D. Handbook of Chemical Property
Estimation Methods. Chapter 2 xe2x80x9cSolubility in Waterxe2x80x9d. McGraw Hill Book Co., New York, 1982). The QSAR database used to calculate the water solubility assessment is maintained by the Institute for Process Analysis, Montana State University (Bozeman, Mont., USA) and accessed through Tymnet Data Systems and Numerica Online Systems (Numericom. 1994. The Online Interface for Numerica Users. Technical Data Base Services, Inc. (TDS, 135 West 50th Street, New York, N.Y. 10020). Some water solubilities are presented in Table A.
A second polymeric component may, optionally, be added to the aqueous coating composition to form a blend. The second polymeric component may be soluble, insoluble, or partially soluble in water. There may be more than one second polymeric component. When such blends are formed, the weight ratio of the polymeric particles to the second polymeric component is 1/19 to 999/1, preferably 1/19 to 19/1, more preferably 1/4 to 9/1, and most preferably 3/7 to 4/1.
The primary criterion for the second polymeric component is that it be dispersed in water, dispersible in water, soluble in water, or partially soluble in water, so that it may be blended with the other components of the aqueous coating composition. When the second polymeric component is insoluble, it will usually be dispersed in water as particles. Although particles of the second polymeric component will often be present in the aqueous coating compositions, the term xe2x80x9cpolymeric particlesxe2x80x9d used herein is reserved for the particles containing both polymer A and polymer B. When the second polymeric component is intended to function as a binder to facilitate film formation during preparation of the coating, it is preferred that its Tg be xe2x88x9240xc2x0 C. to 70xc2x0 C. The second polymeric component could be prepared by any number of polymerization methods including emulsion, suspension, bulk, and solution polymerization. There are no particular compositional constraints for the second polymeric component. The monomers used to prepare the second polymeric component may be those polymerizable by free radical techniques (i.e., including any of those listed above for use in preparing the polymeric particles), or other techniques such as are involved in condensation polymerization. Typically, condensation polymers are prepared, by methods well known in the art, from reactive pairs of monomers, each of which is di-functional or multi-functional. Monomer pairs used to prepare condensation polymers include, for example: acid chlorides and amines; isocyanates and amines; and isocyanates and alcohols. The second polymeric component may also be a polyolefin such as, for example, is formed from the polymerization of ethylene, propylene, higher alkenes, and combinations thereof. The polyolefin may also contain, as polymerized units, conjugated dienes, non-conjugated dienes and functionalized alkenes. The methods of preparing polyolefins are well known in the art, and include Ziegler-Natta and metallocene techniques.
One or more nonionic surfactants may be added to the aqueous coating composition containing the polymeric particles to achieve further improvement of adhesion of subsequently formed coatings to friable surfaces. An effective amount of nonionic surfactant is 0.1-10 weight percent, preferably 0.25-10 weight percent, more preferably 0.5-8 weight percent, and most preferably 1-8 weight percent, calculated as dry weight of surfactant based on the total dry weight of the polymeric particles.
The nonionic surfactant includes those listed hereinabove as providing stabilization during emulsion polymerization. The nonionic surfactant is, preferably, chosen from the group including alkylphenol alkoxylates, alkoxylated amines, and alkyl alcohol alkoxylates. The nonionic surfactant is, more preferably, chosen from the group including alkylphenol ethoxylates, ethoxylated amines, alkyl alcohol ethoxylates, and mixtures thereof.
Useful alkylphenol alkoxylates have the general structure
Rxe2x80x3xe2x80x94Phxe2x80x94Oxe2x80x94(RxO)xe2x80x94Rxe2x80x2xe2x80x94OH, 
where Ph is a phenyl group; R is C1-C4 alkyl or mixtures thereof, mixtures disposed randomly or in sequences (blocks), preferably ethyl; Rxe2x80x2 is C1-C5 alkyl; Rxe2x80x3 is C1-C24 alkyl; and xe2x80x9cxxe2x80x9d is preferably 1 to 100, more preferably 4 to 50, and most preferably 6-50. Alkylphenol alkoxylates include polyoxyethylene nonylphenol ethers, polyoxyethylene octylphenol ethers, tert-octylphenoxyethylpoly(39)ethoxyethanol, and nonylphenoxyethylpoly(40)ethoxyethanol. TRITON(trademark) X-405 (70% aqueous), an alkylphenol ethoxylate, is available from Union Carbide Corporation.
Used herein, xe2x80x9calkoxylated aminexe2x80x9d refers to an amine, the amine nitrogen of which is substituted with one, two, or three xe2x80x94(RO)xRxe2x80x2 groups, where R is C1-C4 alkyl or mixtures thereof, mixtures disposed randomly or in sequences (blocks), preferably ethyl, and where x is from 5-100. Further, the amine nitrogen may be substituted with 0-2 Rxe2x80x3 groups, where Rxe2x80x3 is a C1-C24 alkyl, aralkyl, or aromatic group, preferably each Rxe2x80x3 group is a C1-C24 alkyl selected such that the Iodine number of the water-soluble alkoxylated amine is less than 30, more preferably such that the Iodine number of the water-soluble alkoxylated amine is less than 15, in order to minimize the color of the alkoxylated amine. Preferred are tertiary amines, also referred to herein as t-amines. In any event, the alkoxylated amine is water-soluble at least to the amount that it is utilized in the aqueous coating composition at 25xc2x0 C. Typical alkoxylated amines are the commercially available alkoxylated t-amines, ETHOX(trademark) SAM-50, ETHOMEEN(trademark) 18/25, and the primary alkoxylated amine, JEFFAMINE(trademark) M-2070. ETHOMEEN(trademark) 18/60 (33% aqueous), an ethoxylated tertiary amine, is available from Akzo Nobel Chemical, Inc.
Useful alkyl alcohol alkoxylates have the general structure
Rxe2x80x3xe2x80x94Oxe2x80x94(RxO)xe2x80x94Rxe2x80x2xe2x80x94OH, 
where R is C1-C4 alkyl or mixtures thereof, mixtures disposed randomly or in sequences (blocks), preferably ethyl; Rxe2x80x2 is C1-C5 alkyl; Rxe2x80x3 is C1-C30 alkyl; and xe2x80x9cxxe2x80x9d is preferably 1 to 100, more preferably 4 to 50, and most preferably 6-50. They include polyoxyethylene higher alcohol ethers such as, for example, polyoxyethylene lauryl ethers, polyoxyethylene stearyl ethers, and TERGITOL(trademark) 15-S-40 (25% aqueous), an alkyl alcohol ethoxylate available from Union Carbide Corporation.
The aqueous coating composition of this invention may contain typical coating additives such as binders, fillers, defoamers, cross-linkers, catalysts, surfactants, stabilizers, anti-flocculants, tackifiers, coalescents, colorants, waxes, and pigments. It may be applied to the substrate surface by methods well known in the art such as air-assisted spray, airless spray, plural component spray, brush, roller, squeegee, and the like.
All ranges used herein are inclusive and combinable.
Used herein, the following abbreviations and terms have these meanings:
AAEMxe2x89xa12-(Acetoacetoxy)ethyl methacrylate
ALS=Ammonium Lauryl Sulfate (28% active)
BAxe2x89xa1Butyl Acrylate
MAAxe2x89xa1Methacrylic Acid
MMAxe2x89xa1Methyl Methacrylate
n-DDMxe2x89xa1n-Dodecyl Mercaptan
SLSxe2x89xa1Sodium Lauryl Sulfate (28% active)
STYxe2x89xa1Styrene
VAxe2x89xa1Vinyl Acetate
Empl. No.xe2x89xa1example number
PEAxe2x89xa1pre-emulsion A
PEBxe2x89xa1pre-emulsion B
PVCxe2x89xa1pigment volume concentration
P.S.xe2x89xa1particle size in nanometers (nm)
redoxxe2x89xa1reduction/oxidation (e.g., redox initiation system for polymerization)
volume solidsxe2x89xa1the portion of the total volume of the aqueous dispersion that is occupied by nonvolatile material.
//xe2x89xa1when used in the tables below, xe2x80x9c//xe2x80x9d is inserted between the compositions for each polymerization stage. For example, 50(60 X/40 Y)//50(90 X/10 Z) denotes that the polymerization is carried out in two stages, in the order given. The ratio of those stages is 50/50; the ratio of monomer X to monomer Y in the first polymerization stage is 60/40; the ratio of monomer X to monomer Z in the second polymerization stage is 90/10.
ATTAGEL(trademark) 50 is available from Engelhard Minerals and Chemicals Corp., Houston, Tex.
ACRYSOL(trademark) RM-2020NPR is available from Rohm and Haas Company, Philadelphia, Pa.
BUBBLEBREAKER(trademark) 625 is available from Witco Corp., Phillipsburg, N.J.
ETHOMEEN(trademark) 18/60 is an alkoxylated t-amines, available from Akzo Nobel Chemicals Inc., Charlestown, N.H.
MINEX(trademark) 4 is available from Unimin Specialty Minerals Inc., Tamms, Ill.
NATROSOL(trademark) 250 HBR is available from Hercules Incorporated, New York, N.Y.
TAMOL(trademark) 1124 is a surfactant available from Rohm and Haas Company, Philadelphia, Pa.
TERGITOL(trademark) 15-S-40 is C11-C15 secondary alcohol ethoxylate available from Union Carbide of Danbury, Conn.
TEXANOL(trademark) is available from Eastman Chemicals, Eastman, Tenn.
TI-PURE(trademark) R-902 is titanium dioxide, available from DuPont Company of Wilmington, Del.